A Fast-Digital Current Regulator Based on Matched Pole–Zero Discretization for PMSM

Continuous-time methods design the synchronous-frame current regulator in the S-domain and then discretize it into the Z-domain using the Tustin or Euler method for digital implementation. This process causes discretization errors that significantly impair the performance of permanent magnet synchronous motor (PMSM) drives, especially at a low sampling-to-fundamental frequency ratio (SFR). A direct discrete-time method designs the current regulator directly in the Z-domain with improved dynamic performances. However, it results in online calculations of exponential terms that increase the execution time of the control loop, particularly for interior PMSM (IPMSM). Therefore, this article proposes a novel design approach for a digital current regulator with a high discretization accuracy and fast execution time. The proposed method is a combination of the multiple-input-multiple-output (MIMO) decoupling and matching pole-zero (MPZ) discretization concepts. MIMO decoupling is used to cancel accurately the poles of the plant that migrate with the motor’s speed/frequency change in the S-domain. The MPZ method is used to discretize the current regulator accurately from the S-domain to the Z-domain. A new approximation concept for the calculation of the exponential matrix is adopted to reduce the complexity of the proposed approach. Thus, with the synthesized current regulator, the execution time is reduced significantly compared to the direct discrete-time design methods while keeping the same decoupling and dynamic performances even under low SFRs. Simulations and experiments performed on IPMSM drives have successfully verified the proposed design method, and results show improved decoupling performance and robustness against the variation of parameters with better current harmonic distortion.